Absorptive pigments comprising graphenic carbon particles

ABSTRACT

Thermally produced graphenic carbon particles for use as absorptive pigments are disclosed. The pigments may be used in coatings and bulk articles to provide favorable absorbance characteristics at various wavelengths including visible and infrared regions.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional PatentApplication Ser. No. 62/298,651 filed Feb. 23, 2016, which isincorporated herein by reference. This application is acontinuation-in-part of U.S. patent application Ser. No. 14/979,173,filed Dec. 22, 2015, which is a continuation of PCT International PatentApplication Serial No. PCT/US2015/057858 filed Oct. 28, 2015, whichclaims the benefit of U.S. Provisional Application Ser. No. 62/122,720filed Oct. 28, 2014. The Ser. No. 14/979,173 application is also acontinuation-in-part of U.S. patent application Ser. No. 14/348,280filed Mar. 28, 2014, now issued as U.S. Pat. No. 9,221,688 issued Dec.29, 2015, which is a national phase of PCT International PatentApplication Serial No. PCT/US2012/057811 filed Sep. 28, 2012. PCTInternational Patent Application Serial No. PCT/US2012/057811 is acontinuation-in-part of U.S. patent application Ser. No. 13/249,315filed Sep. 30, 2011, now U.S. Pat. No. 8,486,363 issued Jul. 16, 2013,and is also a continuation-in-part of U.S. patent application Ser. No.13/309,894 filed Dec. 2, 2011, now U.S. Pat. No. 8,486,364 issued Jul.16, 2013. The Ser. No. 14/979,173 application is also acontinuation-in-part of U.S. patent application Ser. No. 14/337,427filed Jul. 22, 2014, now U.S. Pat. No. 9,475,946 issued Oct. 25, 2016,which is a continuation-in-part of U.S. patent application Ser. No.14/348,280 filed Mar. 28, 2014. U.S. patent application Ser. No.14/348,280 is a national phase of PCT International Patent ApplicationSerial No. PCT/US2012/057811. U.S. patent application Ser. No.14/337,427 filed Jul. 22, 2014, is a continuation-in-part of U.S. patentapplication Ser. No. 14/100,064 filed Dec. 9, 2013, now U.S. Pat. No.9,574,094 issued Feb. 21, 2017. U.S. patent application Ser. No.13/309,894 filed Dec. 2, 2011 is a continuation-in-part of U.S. patentapplication Ser. No. 13/249,315 filed Sep. 30, 2011. All of theseapplications and patents are incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to the use of graphenic carbon particlesas absorptive pigments.

BACKGROUND OF THE INVENTION

Specialty carbon blacks are used as absorptive pigments for manyapplications. They have good electromagnetic radiation absorption acrossthe visible spectrum and in to the infrared (IR) and ultraviolet (UV)regions, have good durability, and are relatively inexpensive. However,carbon black pigments may not provide optimal electromagnetic radiationabsorbing properties.

SUMMARY OF THE INVENTION

An aspect of the invention provides an absorptive coating comprising aresin film, and an absorptive pigment comprising thermally producedgraphenic carbon particles in an amount up to 20 weight percent based onthe total dry film weight of the coating, wherein the absorptive coatinghas a minimum absorbance of 80 percent throughout a wavelength range of400 to 1,400 nm.

Another aspect of the invention provides an absorptive coatingcomposition comprising a solvent, a film-forming resin and thermallyproduced graphenic carbon particles in an amount up to 20 weight percentof the total solids weight of the film-forming resin and the thermallyproduced graphenic carbon particles, wherein the absorptive coatingcomposition has a minimum absorbance of 80 percent throughout awavelength range of 400 to 1,400 nm when cured.

Another aspect of the invention provides an article comprising a matrixmaterial and an absorptive pigment dispersed in the matrix materialcomprising thermally produced graphenic carbon particles in an amount upto 20 weight percent based on the total weight of the matrix materialand the thermally produced graphenic carbon particles, wherein thearticle has a minimum absorbance of 80 percent throughout a wavelengthrange of 400 to 1,400 nm.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partially schematic side sectional view of an articlecomprising thermally produced graphenic carbon particles disbursed in amatrix material in accordance with an embodiment of the presentinvention.

FIGS. 2-4 are partially schematic side sectional views of coatingsapplied to substrates, including coating layers comprising grapheniccarbon particles that act as absorptive pigments in accordance withembodiments of the present invention.

FIG. 5 is a graph of absorbance versus wavelengths within the visibleregion of the electromagnetic spectrum, showing increased absorbance forcoatings of the present invention comprising thermally producedgraphenic particles in comparison with coatings comprising carbon blackpigment particles.

FIG. 6 is a photograph of dark coatings of the present inventioncomprising thermally produced graphic carbon particles in comparisonwith lighter coatings comprising carbon black pigments.

FIGS. 7 and 8 are back-lit photographs of a coating of the presentinvention containing an absorptive pigment comprising thermally producedgraphenic particles in comparison with a coating containing carbon blackpigment particles.

FIG. 9 is a graph of absorbance versus wavelength ranges in theultraviolet, visible and near infrared regions of the electromagneticspectrum, showing good absorbance in those regions for thermallyproduced graphenic carbon particles of the present invention dispersedin a solvent.

FIG. 10 is a graph of absorbance versus wavelength ranges in theultraviolet, visible and near infrared regions of the electromagneticspectrum, showing increased absorbance in those regions for a thermallyproduced graphenic carbon particle dispersion of the present inventionin comparison with dispersions of non-thermally produced grapheniccarbon particles made from exfoliated graphite.

DETAILED DESCRIPTION

FIGS. 1-4 schematically illustrate the use of absorptive thermallygraphenic carbon particles in various materials in accordance withembodiments of the present invention. As shown in FIG. 1, thermallygraphenic carbon particles 10 may be dispersed in a matrix material 12such as polymers, glass, ceramics and liquids in order to increaseabsorbance in the materials. The produced graphenic carbon particles maybe provided in any desired loading amounts in the matrix material, forexample, from 0.001 to 30 weight percent based on the total weight ofthe matrix material and the graphenic carbon particles, e.g., from 0.01to 20 weight percent, or from 0.05 to 5 or 10 weight percent, or from0.1 to 2 or 3 weight percent. Examples of matrix materials or articlescontaining graphenic carbon particles dispersed therein include:extruded or molded thermoset or thermoplastic polymers for use inindustries such as construction, transportation, electronic devices andthe like; glass for use in industries such as automotive, construction,aircraft, watercraft and the like; coatings for use in industries suchas architectural, automotive, aerospace, consumer electronics and thelike; and inks for use in industries such as documents, billboards,barcoding and the like. Such articles may be of varying dimensions. Forexample, bulk articles may have length, width, and/or height dimensionsof greater than 100 microns, or greater than 1 micron, or greater than 1mm, or greater than 1 cm, or greater than 10 cm. Coatings and inks mayhave thicknesses of less than 1 micron up to 100 microns or more, forexample, from 1 to 50 microns, or from 2 to 40 microns, or from 3 to 30microns.

As shown in FIG. 2, an absorptive coating 20 comprising thermallyproduced graphenic carbon particles 22 dispersed therein may be appliedonto a substrate 24. Examples of suitable substrates include: polymerssuch as polyethylene terephthalate, polyethylene, polypropylene and thelike; glass; alumina; and metals such as steel and aluminum. Examples ofindustrial uses for such absorptive coatings include decorative, lightblocking, UV protection, heat absorbing and the like.

As shown in FIG. 3, a top absorptive coating 20 comprising thermallyproduced graphenic carbon particles 22 is provided over an intermediateunderlying coating 30, which is deposited on a substrate 24. Examples ofintermediate coatings 30 include electrode position coatings, primercoatings, color coatings and the like. Examples of substrates 24 includemetals such as steel and aluminum, polymers such as polypropylene, andthe like. Industrial uses for such absorptive top coatings withintermediate coating(s) underneath include automobile coatings,aerospace coatings, industrial coatings and the like.

As shown in FIG. 4, an intermediate absorptive coating 20 containingthermally produced graphenic carbon particles 22 is deposited on asubstrate 24 to form an underlying absorptive coating layer, with a topcoating 32 applied over the absorptive coating layer 20. The thermallyproduced graphenic carbon particle-containing underlying coating 20 mayinclude any suitable type of resin and/or binder, as more fullydescribed below. The substrate 24 may comprise any suitable types ofmaterials, such as the substrate materials described above. The topcoating 32 may comprise any desired coating or coatings such as paints,clearcoats and the like typically used for various applicationsincluding automotive, architectural, aerospace, industrial and the like.In certain embodiments, in addition to the coating layers shown in FIG.4, a primer layer, electrodeposited layer or the like may be allied onthe substrate under the intermediate absorptive coating.

In the embodiments shown in FIGS. 2-4, the thicknesses of eachabsorptive coating layer and other layers may be selected as describedin more detail below.

In accordance with embodiments of the invention, thermally producedgraphenic carbon particles provide favorable properties when used asabsorptive pigments, i.e., the graphenic carbon particle pigmentsprovide a favorable combination of reduced reflectance in the visiblespectrum and near IR spectrum, as well as a neutral visual appearance ofany light throughout the visible spectrum that may be reflected from thecoating or article containing the graphenic carbon particles. Thethermally produced graphenic carbon particles may provide extremely goodabsorption across the UV, visible and/or IR spectrums, e.g., strongerand more uniform than carbon blacks. Pigments comprising the grapheniccarbon particles therefore give visual hiding and desirable near IRabsorbance at substantially lower loadings than carbon black. Suchopacity/hiding at lower levels than carbon black provides advantagessuch as weight savings and formulation freedom. In addition, thegraphenic carbon particles may be produced at relatively low cost toprovide low cost pigments.

As used herein, the term “coating” includes resinous and non-resinousfilms, inks, waxes and the like in which thermally produced grapheniccarbon particle pigments may be dispersed. The dry film thickness of thecoatings may typically range from less than 0.5 microns to 100 micronsor more, for example, from 1 to 50 microns. As a particular example, thecured coating thickness may range from 1 to 15 or 20 microns. However,significantly greater coating thicknesses, and significantly greatermaterial dimensions for non-coating materials, are within the scope ofthe invention.

In certain embodiments, the thermally produced graphenic carbon particlepigments may be used in coatings to provide desired absorbancecharacteristics various regions of the electromagnetic spectrum,including in the visible spectrum, e.g., wavelengths from 400 to 700 nm,and/or in the IR or UV regions, and/or in the microwave region. Theabsorbance may be measured throughout the UV range (e.g., from 100 to400 nm), visible range from 400 to 700 nm, the near IR range (e.g., from780 to 3,000 nm), the mid IR range (e.g., 5 to 25 microns), and/or thefar IR range (e.g., 25 to 200 microns). In certain embodiments, theabsorbance within a selected wavelength range may typically be at least30 percent, at least 50 percent, at least 70 percent, at least 80percent, at least 85 percent, or at least 90 percent. For example, whenthe present thermally produced graphenic carbon particles are used asabsorptive pigments in coatings, the absorbance throughout the visiblerange and a portion of the near IR range from 400 to 1,400 nm may be atleast 80 percent, or at least 85 percent, or at least 90 percent, or atleast 95 percent at all wavelengths within the visible range. However,for certain applications, lower absorbance in the visible range may bedesired, e.g., at relatively low loadings of the pigment particles.Furthermore, the variation of absorbance at specific wavelengths withina particular range of wavelengths may be reduced in accordance withembodiments of the invention. For example, the highest and lowestabsorbance values for specific wavelengths within the 400 to 1,400 nmrange may be within 15 percent of each other, or within 10 percent ofeach other, or within 5 percent of each other.

The absorbance of coatings may be dependent on the thickness of aparticular coating, and the absorbance may be defined in terms of astandard film thickness at a given loading of graphenic carbonparticles. As used herein, the term “minimum absorbance” means theminimum quantity of incident electromagnetic radiation, throughout aspecified wavelength range, that is neither reflected nor transmitted bythe sample and is measured by a protocol as described in Example 8herein. As used herein, the term “minimum absorbance throughout awavelength range of 400 to 1,400 nm” is defined and measured asdescribed in Example 8 herein for a coating having a standard dry filmthickness of 20 microns at a pigment particle loading of 0.5 weightpercent based on the dry film weight of the standard 20 micron-thickcoating. Thus, for a coating having a minimum absorbance of 80 percentthroughout a wavelength of 400 to 1,400 nm, the absorbance is measuredbased on a standard coating of the same composition having a dry filmthickness of 20 microns and a graphenic carbon particle loading of 0.5weight percent based on the dry film weight of the standard coating,although the actual coating may have a different thickness and/or adifferent graphenic carbon particle loading than the standard coating.

The amount or loading of thermally produced graphenic carbon particlescontained in the coatings in accordance with certain embodiments may beless than 20 weight percent based on the total dry film weight of thecoating. For example, the graphenic carbon particles may comprise from0.01 to 20 weight percent, or 0.02 to 10 weight percent, or from 0.05 to5 weight percent, or from 0.1 to 2 weight percent of the total dry filmweight of the coating. In certain embodiments, the amount of grapheniccarbon particles contained in the coatings may be relatively low whileproviding the desired level of jetness. For example, the grapheniccarbon particles may comprise less than 5 weight percent, less than 3weight percent, less than 2 weight percent, or less than 1 weightpercent, based on the total dry film weight of the coating. Theparticles may be dispersed uniformly through the coating, ornon-uniformly, e.g., the particles may have a graded concentrationthrough the thickness of the film coating.

In certain embodiments, the coatings may be made from coatingcompositions comprising thermally produced graphenic carbon particlesdispersed within a curable coating composition comprising a solvent anda matrix material such as a film-forming resin or the like in amounts offrom 0.01 to 20 weight percent based on the total solids of the coatingcomposition. For example, the graphenic carbon particles may comprisefrom 0.02 to 10 weight percent, or from 0.05 to 5 weight percent, orfrom 0.01 to 2 weight percent of the solids weight of the coatingcomposition.

In certain embodiments, thermally produced graphenic carbon particlesmay be dispersed in monolithic materials or articles rather than as acoating. In such embodiments, the graphenic carbon particles may bedispersed uniformly throughout the material, or may be dispersednon-uniformly, e.g., with graded loadings throughout the material. Insuch embodiments, the thermally produced graphenic carbon particles maytypically comprise from 0.001 to 20 weight percent of the bulk material,based on the total weight of the material. For example, the grapheniccarbon particles may comprise from 0.01 to 10 weight percent, or from0.02 to 5 weight percent, or from 0.05 to 2 weight percent of thematerial.

The resinous coating compositions can comprise any of a variety ofthermoplastic and/or thermosetting compositions known in the art. Forexample, the coating compositions can comprise film-forming resinsselected from epoxy resins, acrylic polymers, polyester polymers,polyurethane polymers, polyamide polymers, polyether polymers, bisphenolA based epoxy polymers, polysiloxane polymers, styrenes, ethylenes,butylenes, copolymers thereof, and mixtures thereof or waxes. Generally,these polymers can be any polymers of these types made by any methodknown to those skilled in the art. Such polymers may be solvent borne,water soluble or water dispersible, emulsifiable, or of limited watersolubility. Furthermore, the polymers may be provided in sol gelsystems, may be provided in core-shell polymer systems, or may beprovided in powder form. In certain embodiments, the polymers aredispersions in a continuous phase comprising water and/or organicsolvent, for example emulsion polymers or non-aqueous dispersions.

Thermosetting or curable coating compositions typically comprise filmforming polymers or resins having functional groups that are reactivewith either themselves or a crosslinking agent. The functional groups onthe film-forming resin may be selected from any of a variety of reactivefunctional groups including, for example, carboxylic acid groups, aminegroups, epoxide groups, hydroxyl groups, thiol groups, carbamate groups,amide groups, urea groups, isocyanate groups (including blockedisocyanate groups and tris-alkylcarbamoyltriazine) mercaptan groups,styrenic groups, anhydride groups, acetoacetate acrylates, uretidioneand combinations thereof.

Thermosetting coating compositions typically comprise a crosslinkingagent that may be selected from, for example, aminoplasts,polyisocyanates including blocked isocyanates, polyepoxides,beta-hydroxyalkylamides, polyacids, anhydrides, organometallicacid-functional materials, polyamines, polyamides, and mixtures of anyof the foregoing. Suitable polyisocyanates include multifunctionalisocyanates. Examples of multifunctional polyisocyanates includealiphatic diisocyanates like hexamethylene diisocyanate and isophoronediisocyanate, and aromatic diisocyanates like toluene diisocyanate and4,4′-diphenylmethane diisocyanate. The polyisocyanates can be blocked orunblocked. Examples of other suitable polyisocyanates includeisocyanurate trimers, allophanates, and uretdiones of diisocyanates.Examples of commercially available polyisocyanates include DESMODURN3390, which is sold by Bayer Corporation, and TOLONATE HDT90, which issold by Rhodia Inc. Suitable aminoplasts include condensates of aminesand or amides with aldehyde. For example, the condensate of melaminewith formaldehyde is a suitable aminoplast. Suitable aminoplasts arewell known in the art. A suitable aminoplast is disclosed, for example,in U.S. Pat. No. 6,316,119 at column 5, lines 45-55, incorporated byreference herein. In certain embodiments, the resin can be selfcrosslinking. Self crosslinking means that the resin contains functionalgroups that are capable of reacting with themselves, such asalkoxysilane groups, or that the reaction product contains functionalgroups that are coreactive, for example hydroxyl groups and blockedisocyanate groups.

In addition to the resin and thermally produced graphenic carbonparticle components, the coating compositions and cured coatings mayinclude additional components conventionally added to coating or inkcompositions, such as cross-linkers, pigments, tints, flow aids,defoamers, dispersants, solvents, UV absorbers, catalysts and surfaceactive agents.

In addition to their use as pigments in coatings, the present thermallyproduced graphenic carbon particles may also be used as absorptivepigments in thermoplastic and/or thermoset plastic bulk articles. Inthis embodiment, the thermally produced graphenic carbon particles maybe dispersed uniformly or non-uniformly in a matrix of the thermoplasticor thermoset plastic bulk material. The particles may typically comprisefrom 0.001 to 20 weight percent, or from 0.01 to 10 weight percent ofthe total combined weight of the thermoplastic and/or thermoset plasticand the thermally produced graphenic carbon particles of the bulkarticle. For example, from 0.05 to 5 weight percent or from 0.1 to 2weight percent.

Suitable bulk thermoplastic materials in which the present thermallyproduced graphenic carbon particles may be dispersed as an absorptivepigment include polyethylene, polypropylene, polystyrene,polymethylmethacrylate, polycarbonate, polyvinylchloride,polyethyleneterephthalate, acrylonitrile-butadiene-styrene,polyvinylbutyral, and polyvinylacetate and the like. In certainembodiments, the thermoplastic may comprise polycarbonate, polyethyleneand/or polyvinylchloride.

In certain embodiments, the plastic material in which the thermallyproduced graphenic carbon particles are dispersed as absorptive pigmentsinclude thermoset plastics such as polyurethane, melamine, phenolics,acrylics, polyesters and the like. For example, the thermoset plasticmay comprise melamine, acrylics and/or polyurethane.

As used herein, the term “graphenic carbon particles” means carbonparticles having structures comprising one or more layers ofone-atom-thick planar sheets of sp²-bonded carbon atoms that are denselypacked in a honeycomb crystal lattice. The average number of stackedlayers may be less than 100, for example, less than 50. In certainembodiments, the average number of stacked layers is 30 or less, such as20 or less, 10 or less, or, in some cases, 5 or less. The grapheniccarbon particles may be substantially flat, however, at least a portionof the planar sheets may be substantially curved, curled, creased orbuckled. The particles typically do not have a spheroidal or equiaxedmorphology.

In certain embodiments, the graphenic carbon particles have a thickness,measured in a direction perpendicular to the carbon atom layers, of nomore than 10 nanometers, no more than 5 nanometers, or, in certainembodiments, no more than 4 or 3 or 2 or 1 nanometers, such as no morethan 3.6 nanometers. In certain embodiments, the graphenic carbonparticles may be from 1 atom layer up to 3, 6, 9, 12, 20 or 30 atomlayers thick, or more. In certain embodiments, the graphenic carbonparticles have a width and length, measured in a direction parallel tothe carbon atoms layers, of at least 25 nanometers, such as more than100 nanometers, in some cases more than 100 nanometers up to 500nanometers, or more than 100 nanometers up to 200 nanometers. Thegraphenic carbon particles may be provided in the form of ultrathinflakes, platelets or sheets having relatively high aspect ratios (aspectratio being defined as the ratio of the longest dimension of a particleto the shortest dimension of the particle) of greater than 3:1, such asgreater than 10:1.

In certain embodiments, the graphenic carbon particles have relativelylow oxygen content. For example, the graphenic carbon particles may,even when having a thickness of no more than 5 or no more than 2nanometers, have an oxygen content of no more than 2 atomic weightpercent, such as no more than 1.5 or 1 atomic weight percent, or no morethan 0.6 atomic weight, such as about 0.5 atomic weight percent. Theoxygen content of the graphenic carbon particles can be determined usingX-ray Photoelectron Spectroscopy, such as is described in D. R. Dreyeret al., Chem. Soc. Rev. 39, 228-240 (2010).

In certain embodiments, the graphenic carbon particles have a B.E.T.specific surface area of at least 50 square meters per gram, such as 70to 1000 square meters per gram, or, in some cases, 200 to 1000 squaremeters per grams or 200 to 400 square meters per gram. As used herein,the term “B.E.T. specific surface area” refers to a specific surfacearea determined by nitrogen adsorption according to the ASTMD 3663-78standard based on the Brunauer-Emmett-Teller method described in theperiodical “The Journal of the American Chemical Society”, 60, 309(1938).

In certain embodiments, the graphenic carbon particles have a Ramanspectroscopy 2D/G peak ratio of at least 0.9:1, or at least 0.95:1, orat least 0.95:1, or at least 1.1, for example, at least 1.1:1 or 1.2:1or 1.3:1. As used herein, the term “2D/G peak ratio” refers to the ratioof the intensity of the 2D peak at 2692 cm⁻¹ to the intensity of the Gpeak at 1,580 cm⁻¹.

In certain embodiments, the graphenic carbon particles have a relativelylow bulk density. For example, the graphenic carbon particles arecharacterized by having a bulk density (tap density) of less than 0.2g/cm³, such as no more than 0.1 g/cm³. For the purposes of the presentinvention, the bulk density of the graphenic carbon particles isdetermined by placing 0.4 grams of the graphenic carbon particles in aglass measuring cylinder having a readable scale. The cylinder is raisedapproximately one-inch and tapped 100 times, by striking the base of thecylinder onto a hard surface, to allow the graphenic carbon particles tosettle within the cylinder. The volume of the particles is thenmeasured, and the bulk density is calculated by dividing 0.4 grams bythe measured volume, wherein the bulk density is expressed in terms ofg/cm³.

In certain embodiments, the graphenic carbon particles have a compresseddensity and a percent densification that is less than the compresseddensity and percent densification of graphite powder and certain typesof substantially flat graphenic carbon particles such as those formedfrom exfoliated graphite. Lower compressed density and lower percentdensification are each currently believed to contribute to betterdispersion and/or rheological properties than graphenic carbon particlesexhibiting higher compressed density and higher percent densification.In certain embodiments, the compressed density of the graphenic carbonparticles is 0.9 or less, such as less than 0.8, less than 0.7, such asfrom 0.6 to 0.7. In certain embodiments, the percent densification ofthe graphenic carbon particles is less than 40%, such as less than 30%,such as from 25 to 30%.

For purposes of the present invention, the compressed density ofgraphenic carbon particles is calculated from a measured thickness of agiven mass of the particles after compression. Specifically, themeasured thickness is determined by subjecting 0.1 grams of thegraphenic carbon particles to cold press under 15,000 pounds of force ina 1.3 centimeter die for 45 minutes, wherein the contact pressure is 500MPa. The compressed density of the graphenic carbon particles is thencalculated from this measured thickness according to the followingequation:

${{Compressed}\mspace{14mu} {Density}\mspace{14mu} \left( {g\text{/}{cm}^{3}} \right)} = \frac{0.1\mspace{14mu} {grams}}{\Pi*\left( {1.3\mspace{14mu} {cm}\text{/}2} \right)^{2}*\left( {{measured}\mspace{14mu} {thickness}\mspace{14mu} {in}\mspace{14mu} {cm}} \right)}$

The percent densification of the graphenic carbon particles is thendetermined as the ratio of the calculated compressed density of thegraphenic carbon particles, as determined above, to 2.2 g/cm³, which isthe density of graphite.

In certain embodiments, the graphenic carbon particles have a measuredbulk liquid conductivity of at least 100 microSiemens, such as at least120 microSiemens, such as at least 140 microSiemens immediately aftermixing and at later points in time, such as at 10 minutes, or 20minutes, or 30 minutes, or 40 minutes. For the purposes of the presentinvention, the bulk liquid conductivity of the graphenic carbonparticles is determined as follows. First, a sample comprising a 0.5%solution of graphenic carbon particles in butyl cellosolve is sonicatedfor 30 minutes with a bath sonicator. Immediately following sonication,the sample is placed in a standard calibrated electrolytic conductivitycell (K=1). A Fisher Scientific AB 30 conductivity meter is introducedto the sample to measure the conductivity of the sample. Theconductivity is plotted over the course of about 40 minutes.

The morphology of the graphenic carbon particles may also be measured interms of a dibutyl phthalate absorption number (DBPA) in accordance withthe standard ASTM D2414 test. DBP absorption may be used to measure therelative structure of graphenic carbon particles by determining theamount of DBP a given mass of graphenic carbon particles can absorbbefore reaching a specific viscous paste. In accordance with certainembodiments, the DBPA of the thermally produced graphenic carbonparticles may typically be at least 200, for example, from 200 to 800,or from 300 to 500.

In accordance with certain embodiments, percolation, defined as longrange interconnectivity, occurs between the conductive graphenic carbonparticles. Such percolation may reduce the resistivity of the coatingcompositions. The conductive graphenic particles may occupy a minimumvolume within the coating such that the particles form a continuous, ornearly continuous, network. In such a case, the aspect ratios of thegraphenic carbon particles may affect the minimum volume required forpercolation.

In certain embodiments, at least a portion of the graphenic carbonparticles to be dispersed in the compositions of the present inventionmay be made by thermal processes. In accordance with embodiments of theinvention, thermally produced graphenic carbon particles are made fromcarbon-containing precursor materials that are heated to hightemperatures in a thermal zone such as a plasma. As more fully describedbelow, the carbon-containing precursor materials are heated to asufficiently high temperature, e.g., above 3,500° C., to producegraphenic carbon particles having characteristics as described above.The carbon-containing precursor, such as a hydrocarbon provided ingaseous or liquid form, is heated in the thermal zone to produce thegraphenic carbon particles in the thermal zone or downstream therefrom.For example, thermally produced graphenic carbon particles may be madeby the systems and methods disclosed in U.S. Pat. Nos. 8,486,363 and8,486,364.

In certain embodiments, the thermally produced graphenic carbonparticles may be made by using the apparatus and method described inU.S. Pat. No. 8,486,363 at [0022] to [0048] in which (i) one or morehydrocarbon precursor materials capable of forming a two-carbon fragmentspecies (such as n-propanol, ethane, ethylene, acetylene, vinylchloride, 1,2-dichloroethane, allyl alcohol, propionaldehyde, and/orvinyl bromide) is introduced into a thermal zone (such as a plasma), and(ii) the hydrocarbon is heated in the thermal zone to form the grapheniccarbon particles. In other embodiments, the thermally produced grapheniccarbon particles may be made by using the apparatus and method describedin U.S. Pat. No. 8,486,364 at [0015] to [0042] in which (i) a methaneprecursor material (such as a material comprising at least 50 percentmethane, or, in some cases, gaseous or liquid methane of at least 95 or99 percent purity or higher) is introduced into a thermal zone (such asa plasma), and (ii) the methane precursor is heated in the thermal zoneto form the graphenic carbon particles. Such methods can producegraphenic carbon particles having at least some, in some cases all, ofthe characteristics described above.

During production of the graphenic carbon particles by the thermalproduction methods described above, a carbon-containing precursor isprovided as a feed material that may be contacted with an inert carriergas. The carbon-containing precursor material may be heated in a thermalzone, for example, by a plasma system. In certain embodiments, theprecursor material is heated to a temperature of at least 3,500° C., forexample, from a temperature of greater than 3,500° C. or 4,000° C. up to10,000° C. or 20,000° C. Although the thermal zone may be generated by aplasma system, it is to be understood that any other suitable heatingsystem may be used to create the thermal zone, such as various types offurnaces including electrically heated tube furnaces and the like.

The gaseous stream may be contacted with one or more quench streams thatare injected into the plasma chamber through at least one quench streaminjection port. The quench stream may cool the gaseous stream tofacilitate the formation or control the particle size or morphology ofthe graphenic carbon particles. In certain embodiments of the invention,after contacting the gaseous product stream with the quench streams, theultrafine particles may be passed through a converging member. After thegraphenic carbon particles exit the plasma system, they may becollected. Any suitable means may be used to separate the grapheniccarbon particles from the gas flow, such as, for example, a bag filter,cyclone separator or deposition on a substrate.

In certain embodiments, at least a portion of the thermally producedgraphenic carbon particles as described above may be replaced withgraphenic carbon particles from commercial sources, for example, fromAngstron Materials, XG Sciences and other commercial sources. However,due to the high electromagnetic radiation absorbance of absorptivepigments comprising the thermally produced graphenic carbon particles ofthe present invention, their substitution with commercially availablegraphenic carbon particles may not be optimal for many applications. Insuch embodiments, the commercially available graphenic carbon particlesmay comprise exfoliated graphite and have different characteristics incomparison with the thermally produced graphenic carbon particles, suchas different size distributions, thicknesses, aspect ratios, structuralmorphologies, oxygen contents, and chemical functionalities at the basalplanes/edges. For example, when thermally produced graphenic carbonparticles are combined with commercially available graphenic carbonparticles in accordance with embodiments of the invention, a bi-modaldistribution, tri-modal distribution, etc. of graphenic carbon particlecharacteristics may be achieved. The graphenic carbon particlescontained in the compositions may have multi-modal particle sizedistributions, aspect ratio distributions, structural morphologies, edgefunctionality differences, oxygen content, and the like.

In certain embodiments, the graphenic carbon particles arefunctionalized. As used herein, “functionalized”, when referring tographenic carbon particles, means covalent bonding of any non-carbonatom or any organic group to the graphenic carbon particles. Thegraphenic carbon particles may be functionalized through the formationof covalent bonds between the carbon atoms of a particle and otherchemical moieties such as carboxylic acid groups, sulfonic acid groups,hydroxyl groups, halogen atoms, nitro groups, amine groups, aliphatichydrocarbon groups, phenyl groups and the like. For example,functionalization with carbonaceous materials may result in theformation of carboxylic acid groups on the graphenic carbon particles.The graphenic carbon particles may also be functionalized by otherreactions such as Diels-Alder addition reactions, 1,3-dipolarcycloaddition reactions, free radical addition reactions and diazoniumaddition reactions. In certain embodiments, the hydrocarbon and phenylgroups may be further functionalized. If the graphenic carbon particlesalready have some hydroxyl functionality, the functionality can bemodified and extended by reacting these groups with, for example, anorganic isocyanate.

In certain embodiments, coating compositions or other types ofcompositions in which the present absorptive pigments are dispersed maybe produced by initially dispersing the graphenic carbon particles in acarrier. Such dispersions may comprise: (a) graphenic carbon particlessuch as any of those described above; (b) a carrier that may be selectedfrom water, at least one organic solvent, or combinations of water andat least one organic solvent; (c) at least one polymeric dispersant,such as the copolymer described generally below; and, optionally, (d) atleast one resin as described above or other additives.

Certain compositions comprise at least one polymeric dispersant. Incertain embodiments, such a polymeric dispersant comprises a tri-blockcopolymer comprising: (i) a first segment comprising graphenic carbonaffinic groups, such as hydrophobic aromatic groups; (ii) a secondsegment comprising polar groups, such as hydroxyl groups, amine groups,ether groups, and/or acid groups; and (iii) a third segment which isdifferent from the first segment and the second segment, such as asegment that is substantially non-polar, i.e., substantially free ofpolar groups. As used herein, term “substantially free” when used withreference to the absence of groups in a polymeric segment, means that nomore than 5% by weight of the monomer used to form the third segmentcomprises polar groups.

Suitable polymeric dispersants include acrylic copolymers produced fromatom transfer radical polymerization. In certain embodiments, suchcopolymers have a weight average molecular weight of 1,000 to 20,000.

In certain embodiments, the polymeric pigment dispersant has a polymerchain structure represented by the following general formula (I),

Φ−(G)_(p)−(W)_(q)−(Y)_(s)T  (I)

wherein G is a residue of at least one radically polymerizableethylenically unsaturated monomer; W and Y are residues of at least oneradically polymerizable ethylenically unsaturated monomer with W and Ybeing different from one another; Y is optional; Φ is a hydrophobicresidue of or derived from an initiator and is free of the radicallytransferable group; T is or is derived from the radically transferablegroup of the initiator; p, q and s represent average numbers of residuesoccurring in a block of residues; p, q and s are each individuallyselected such that the polymeric dispersant has a number averagemolecular weight of at least 250.

The polymeric dispersant may be described generally as having a head andtail structure, i.e., as having a polymeric head portion and a polymerictail portion. The polymeric tail portion may have a hydrophilic portionand a hydrophobic portion, particularly at the terminus thereof. Whilenot intending to be bound by any theory, it is believed that thepolymeric head portion of the polymeric dispersant can be associatedwith the graphenic carbon particles, while the polymeric tail portionaids in dispersing the graphenic carbon particles and can be associatedwith other components of an ink or coating composition. As used herein,the terms “hydrophobic” and “hydrophilic” are relative to each other.

In certain embodiments, the polymeric dispersant is prepared by atomtransfer radical polymerization (ATRP). The ATRP process can bedescribed generally as comprising: polymerizing one or more radicallypolymerizable monomers in the presence of an initiation system; forminga polymer; and isolating the formed polymer. In certain embodiments, theinitiation system comprises: a monomeric initiator having a singleradically transferable atom or group; a transition metal compound, i.e.,a catalyst, which participates in a reversible redox cycle with theinitiator; and a ligand, which coordinates with the transition metalcompound. The ATRP process is described in further detail inInternational Patent Publication No. WO 98/40415 and U.S. Pat. Nos.5,807,937, 5,763,548 and 5,789,487.

Catalysts that may be used in the ATRP preparation of the polymericdispersant include any transition metal compound that can participate ina redox cycle with the initiator and the growing polymer chain. It maybe preferred that the transition metal compound not form directcarbon-metal bonds with the polymer chain. Transition metal catalystsuseful in the present invention may be represented by the followinggeneral formula (II),

M^(n+)X_(n)  (II)

wherein M is the transition metal; n is the formal charge on thetransition metal having a value of from 0 to 7; and X is a counterion orcovalently bonded component. Examples of the transition metal M include,but are not limited to, Cu, Fe, Au, Ag, Hg, Pd, Pt, Co, Mn, Ru, Mo, Nband Zn. Examples of X include, but are not limited to, halide, hydroxy,oxygen, C₁-C₆-alkoxy, cyano, cyanato, thiocyanato and azido. In onespecific example, the transition metal is Cu(I) and X is halide, forexample, chloride. Accordingly, one specific class of transition metalcatalysts is the copper halides, for example, Cu(I)Cl. In certainembodiments, the transition metal catalyst may contain a small amount,for example, 1 mole percent, of a redox conjugate, for example,Cu(II)Cl₂ when Cu(I)Cl is used. Additional catalysts useful in preparingthe polymeric dispersant are described in U.S. Pat. No. 5,807,937 atcolumn 18, lines 29 through 56. Redox conjugates are described infurther detail in U.S. Pat. No. 5,807,937 at column 11, line 1 throughcolumn 13, line 38.

Ligands that may be used in the ATRP preparation of the polymericdispersant include, but are not limited to, compounds having one or morenitrogen, oxygen, phosphorus and/or sulfur atoms, which can coordinateto the transition metal catalyst compound, for example, through sigmaand/or pi bonds. Classes of useful ligands include, but are not limitedto, unsubstituted and substituted pyridines and bipyridines; porphyrins;cryptands; crown ethers; for example, 18-crown-6; polyamines, forexample, ethylenediamine; glycols, for example, alkylene glycols, suchas ethylene glycol; carbon monoxide; and coordinating monomers, forexample, styrene, acrylonitrile and hydroxyalkyl (meth)acrylates. Asused herein, the term “(meth)acrylate” and similar terms refer toacrylates, methacrylates and mixtures of acrylates and methacrylates.One specific class of ligands is the substituted bipyridines, forexample, 4,4′-dialkyl-bipyridyls. Additional ligands that may be used inpreparing polymeric dispersant are described in U.S. Pat. No. 5,807,937at column 18, line 57 through column 21, line 43.

Classes of monomeric initiators that may be used in the ATRP preparationof the polymeric dispersant include, but are not limited to, aliphaticcompounds, cycloaliphatic compounds, aromatic compounds, polycyclicaromatic compounds, heterocyclic compounds, sulfonyl compounds, sulfenylcompounds, esters of carboxylic acids, nitrites, ketones, phosphonatesand mixtures thereof, each having a radically transferable group, andpreferably a single radically transferable group. The radicallytransferable group of the monomeric initiator may be selected from, forexample, cyano, cyanato, thiocyanato, azido and halide groups. Themonomeric initiator may also be substituted with functional groups, forexample, oxyranyl groups, such as glycidyl groups. Additional usefulinitiators are described in U.S. Pat. No. 5,807,937 at column 17, line 4through column 18, line 28.

In certain embodiments, the monomeric initiator is selected from1-halo-2,3-epoxypropane, p-toluenesulfonyl halide, p-toluenesulfenylhalide, C₆-C₂₀-alkyl ester of alpha-halo-C₂-C₆-carboxylic acid,halomethylbenzene, (1-haloethyl)benzene, halomethylnaphthalene,halomethylanthracene and mixtures thereof. Examples of C₂-C₆-alkyl esterof alpha-halo-C₂-C₆-carboxylic acids include, hexylalpha-bromopropionate, 2-ethylhexyl alpha-bromopropionate, 2-ethylhexylalpha-bromohexionate and icosanyl alpha-bromopropionate. As used herein,the term “monomeric initiator” is meant to be distinguishable frompolymeric initiators, such as polyethers, polyurethanes, polyesters andacrylic polymers having radically transferable groups.

In the ATRP preparation, the polymeric dispersant and the amounts andrelative proportions of monomeric initiator, transition metal compoundand ligand may be those for which ATRP is most effectively performed.The amount of initiator used can vary widely and is typically present inthe reaction medium in a concentration of from 10-4 moles/liter (M) to 3M, for example, from 10-3 M to 10-1 M. As the molecular weight of thepolymeric dispersant can be directly related to the relativeconcentrations of initiator and monomer(s), the molar ratio of initiatorto monomer is an important factor in polymer preparation. The molarratio of initiator to monomer is typically within the range of 10-4:1 to0.5:1, for example, 10-3:1 to 5×10-2:1.

In preparing the polymeric dispersant by ATRP methods, the molar ratioof transition metal compound to initiator is typically in the range of10⁴:1 to 10:1, for example, 0.1:1 to 5:1. The molar ratio of ligand totransition metal compound is typically within the range of 0.1:1 to100:1, for example, 0.2:1 to 10:1.

The polymeric dispersant may be prepared in the absence of solvent,i.e., by means of a bulk polymerization process. Often, the polymericdispersant is prepared in the presence of a solvent, typically waterand/or an organic solvent. Classes of useful organic solvents include,but are not limited to, esters of carboxylic acids, ethers, cyclicethers, C₅-C₁₀ alkanes, C₅-C₈ cycloalkanes, aromatic hydrocarbonsolvents, halogenated hydrocarbon solvents, amides, nitrites,sulfoxides, sulfones and mixtures thereof. Supercritical solvents, suchas CO₂, C₁-C₄ alkanes and fluorocarbons, may also be employed. One classof solvents is the aromatic hydrocarbon solvents, such as xylene,toluene, and mixed aromatic solvents such as those commerciallyavailable from Exxon Chemical America under the trademark SOLVESSO.Additional solvents are described in further detail in U.S. Pat. No.5,807,937, at column 21, line 44 through column 22, line 54.

The ATRP preparation of the polymeric dispersant is typically conductedat a reaction temperature within the range of 25° C. to 140° C., forexample, from 50° C. to 100° C., and a pressure within the range of 1 to100 atmospheres, usually at ambient pressure.

The ATRP transition metal catalyst and its associated ligand aretypically separated or removed from the polymeric dispersant prior toits use in the polymeric dispersants of the present invention. Removalof the ATRP catalyst may be achieved using known methods, including, forexample, adding a catalyst binding agent to the mixture of the polymericdispersant, solvent and catalyst, followed by filtering. Examples ofsuitable catalyst binding agents include, for example, alumina, silica,clay or a combination thereof. A mixture of the polymeric dispersant,solvent and ATRP catalyst may be passed through a bed of catalystbinding agent. Alternatively, the ATRP catalyst may be oxidized in situ,the oxidized residue of the catalyst being retained in the polymericdispersant.

With reference to general formula (I), G may be a residue of at leastone radically polymerizable ethylenically unsaturated monomer, such as amonomer selected from an oxirane functional monomer reacted with acarboxylic acid which may be an aromatic carboxylic acid or polycyclicaromatic carboxylic acid.

The oxirane functional monomer or its residue that is reacted with acarboxylic acid may be selected from, for example, glycidyl(meth)acrylate, 3,4-epoxycyclohexylmethyl(meth)acrylate,2-(3,4-epoxycyclohexyl)ethyl(meth)acrylate, allyl glycidyl ether andmixtures thereof. Examples of carboxylic acids that may be reacted withthe oxirane functional monomer or its residue include, but are notlimited to, napthoic acid, hydroxy napthoic acids, para-nitrobenzoicacid and mixtures thereof.

With continued reference to general formula (I), in certain embodiments,W and Y may each independently be residues of, but are not limited to,methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate,isopropyl (meth)acrylate, n-butyl (meth)acrylate, iso-butyl(meth)acrylate, tert-butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate,lauryl (meth)acrylate, isobornyl (meth)acrylate, cyclohexyl(meth)acrylate, 3,3,5-trimethylcyclohexyl (meth)acrylate, isocane(meth)acrylate, hydroxyethyl (meth)acrylate, hydroxypropyl(meth)acrylate, hydroxybutyl (meth)acrylate, butyl (meth)acrylate,methoxy poly(ethylene glycol) mono(meth)acrylate, poly(ethylene glycol)mono(meth)acrylate, methoxy poly(propylene glycol) mono (meth)acrylate,poly(propylene glycol) mono (meth)acrylate, methoxy copoly(ethyleneglycol/propylene glycol) mono (meth)acrylate, and copoly(ethyleneglycol/propylene glycol) mono (meth)acrylate.

In general formula (I), in certain embodiments, W and Y may eachindependently be residues of monomers having more than one(meth)acryloyl group, such as (meth)acrylic anhydride, diethyleneglycolbis(meth)acrylate,1,4-butanediol diacrylate, 1,6-hexanediol diacrylate,4,4′-isopropylidenediphenol bis(meth)acrylate (Bisphenol Adi(meth)acrylate), alkoxylated 4,4′-isopropylidenediphenolbis(meth)acrylate, trimethylolpropane tris(meth)acrylate, alkoxylatedtrimethylolpropane tris(meth)acrylate, polyethylene glycoldi(meth)acrylate, polypropylene glycol di(meth)acrylate, andcopoly(ethylene glycol/propylene glycol) di(meth)acrylate.

The letters p, q and s represent the average total number of G, W and Yresidues, respectively, occurring per block or segment of G residues(G-block or G-segment), W residues (W-block or W-segment) and Y residues(Y-block or Y-segment), respectively. When containing more than one typeor species of monomer residue, the W- and Y-blocks may each have atleast one of random block (e.g., di-block and tri-block), alternating,and gradient architectures. Gradient architecture refers to a sequenceof different monomer residues that change gradually in a systematic andpredictable manner along the polymer backbone. For purposes ofillustration, a W-block containing 6 residues of butyl methacrylate (BMA) and 6 residues of hydroxy propyl methacrylate (HPMA), for which q is12, may have di-block, tetra-block, alternating and gradientarchitectures as described in U.S. Pat. No. 6,642,301, col. 10, lines5-25. In certain embodiments, the G-block may include about 5-15residues of glycidyl(meth)acrylate) reacted with an aromatic carboxylicacid (such as 3-hydroxy-2-napthoic acid), the W-block may be a randomblock of about 20-30 BMA and HPMA residues and the Y-block may be auniform block of about 5-15 butyl acrylate (BA) residues.

The order in which monomer residues occur along the polymer backbone ofthe polymeric dispersant is typically determined by the order in whichthe corresponding monomers are fed into the vessel in which thecontrolled radical polymerization is conducted. For example, themonomers that are incorporated as residues in the G-block of thepolymeric dispersant are generally fed into the reaction vessel prior tothose monomers that are incorporated as residues in the W-block,followed by the residues of the Y-block.

During formation of the W- and Y-blocks, if more than one monomer is fedinto the reaction vessel at a time, the relative reactivities of themonomers typically determine the order in which they are incorporatedinto the living polymer chain. Gradient sequences of monomer residueswithin the W- and Y-blocks can be prepared by controlled radicalpolymerization, and, in particular, by ATRP methods by (a) varying theratio of monomers fed to the reaction medium during the course of thepolymerization, (b) using a monomer feed containing monomers havingdifferent rates of polymerization, or (c) a combination of (a) and (b).Copolymers containing gradient architecture are described in furtherdetail in U.S. Pat. No. 5,807,937, at column 29, line 29 through column31, line 35.

In certain embodiments, subscripts q and s each have a value of at least1, such as at least 5 for general formula (I). Also, subscript s oftenhas a value of less than 300, such as less than 100, or less than 50(for example 20 or less) for general formula (I). The values ofsubscripts q and s may range between any combination of these values,inclusive of the recited values, for example, s may be a number from 1to 100. Subscript p may have a value of at least 1, such as at least 5.Subscript p also often has a value of less than 300, such as less than100 or less than 50 (e.g., 20 or less). The value of subscript p mayrange between any combination of these values, inclusive of the recitedvalues, for example, p may be a number up to 50. The polymericdispersant often has a number average molecular weight (Mn) of from 250to 40,000, for example, from 1,000 to 30,000 or from 2,000 to 20,000, asdetermined by gel permeation chromatography using polystyrene standards.

Symbol Φ of general formula (I) is, or is derived from, the residue ofthe initiator used in the preparation of the polymeric dispersant bycontrolled radical polymerization, and is free of the radicallytransferable group of the initiator. For example, when the polymericdispersant is initiated in the presence of toluene sulfonyl chloride,the symbol Φ, more specifically Φ−, is the residue,

The symbol Φ may also represent a derivative of the residue of theinitiator.

In general formula (I), T is or is derived from the radicallytransferable group of the ATRP initiator. The residue of the radicallytransferable group may be (a) left on the polymeric dispersant, (b)removed or (c) chemically converted to another moiety. The radicallytransferable group may be removed by substitution with a nucleophiliccompound, for example, an alkali metal alkoxylate. When the residue ofthe radically transferable group is, for example, a cyano group (—CN),it can be converted to an amide group or carboxylic acid group bymethods known in the art.

The polymeric dispersant is typically present in the graphenic carbonparticle dispersion described above in an amount of at least 0.1 percentby weight, such as at least 0.5 percent by weight, or, in some cases, atleast 1 percent by weight, based on the total weight of the grapheniccarbon particle dispersion. The polymeric dispersant may typically bepresent in the graphenic carbon particle dispersion in an amount of lessthan 75 percent by weight, or less than 50 percent by weight, based onthe total weight of the graphenic carbon particle dispersion. In certainembodiments, the polymeric dispersant may be present in the grapheniccarbon particle dispersion in an amount of less than 30 percent byweight, or less than 15 percent by weight, based on the total weight ofthe graphenic carbon particle dispersion.

The graphenic carbon particle dispersion often also comprises at leastwater and/or at least one organic solvent. Classes of organic solventsthat may be present include, but are not limited to, xylene, toluene,alcohols, for example, methanol, ethanol, n-propanol, iso-propanol,n-butanol, sec-butyl alcohol, tert-butyl alcohol, iso-butyl alcohol,furfuryl alcohol and tetrahydrofurfuryl alcohol; ketones orketoalcohols, for example, acetone, methyl ethyl ketone, and diacetonealcohol; ethers, for example, dimethyl ether and methyl ethyl ether;cyclic ethers, for example, tetrahydrofuran and dioxane; esters, forexample, ethyl acetate, ethyl lactate, ethylene carbonate and propylenecarbonate; polyhydric alcohols, for example, ethylene glycol, diethyleneglycol, triethylene glycol, propylene glycol, tetraethylene glycol,polyethylene glycol, glycerol, 2-methyl-2,4-pentanediol and1,2,6-hexantriol; hydroxy functional ethers of alkylene glycols, forexample, butyl 2-hydroxyethyl ether, hexyl 2-hydroxyethyl ether, methyl2-hydroxypropyl ether and phenyl 2-hydroxypropyl ether; nitrogencontaining cyclic compounds, for example, pyrrolidone,N-methyl-2-pyrrolidone and 1,3-dimethyl-2-imidazolidinone; and sulfurcontaining compounds such as thioglycol, dimethyl sulfoxide andtetramethylene sulfone. When the solvent comprises water, it can be usedalone or in combination with organic solvents such as propylene glycolmonomethylether, ethanol and the like.

The graphenic carbon particle dispersion may be prepared by the use ofconventional mixing techniques such as energy intensive mixing orgrinding means, such as ball mills or media mills (e.g., sand mills),attritor mills, 3-roll mills, rotor/stator mixers, high speed mixers,sonicators, and the like.

The graphenic carbon particles may be mixed with film-forming resins andother components of the compositions. For example, for two-part coatingsystems, the graphenic carbon particles may be dispersed into part Aand/or part B. In certain embodiments, the graphenic carbon particlesare dispersed into part A by various mixing techniques such assonication, high speed mixing, media milling and the like. In certainembodiments, the graphenic carbon particles may be mixed into thecoating compositions using high-energy and/or high-shear techniques suchas sonication, 3-roll milling, ball milling, attritor milling,rotor/stator mixers, and the like.

The following examples are intended to illustrate various aspects of thepresent invention, and are not intended to limit the scope of theinvention.

Example 1

A dispersion of thermally produced graphenic carbon particles was madeby adding 54.15 g of solvent-born block copolymer dispersant (whichcomprises 43 weight % n-butyl acetate and 57 weight % block copolymer asdisclosed in U.S. 2008/0188610), 76.45 g of n-butyl acetate, and 11.20 gof thermally produced graphenic carbon particles produced in accordancewith the method disclosed in U.S. Pat. No. 8,486,364 having a measuredBET surface area of 280 m²/g. The ingredients were added to a 16 oz.glass jar. 700 g of 1.0-1.2 mm Zirconox milling media (from JyotiCeramic) was added into the jar. The jar was shaken for 4 hours using aLau disperser (Model DAS 200, Lau, GmbH). The milling media were thenseparated from the dispersion product using paper cone paint filters.Extra n-butyl acetate was added to aid in achieving a higher yield fromthe filtration process. At this point the dispersion had a total solidscontent of 23.89 weight %, a resin solids content of 17.70 weight %, anda graphenic carbon particles content of 6.19 weight %. This dispersionwas then placed into a 1.25 quart stainless steel beaker, which waswrapped with a ¼ inch coil of copper tubing through which water wasflowing at a low rate to achieve cooling of the beaker. 600 g of glassbeads (Duraspheres, GL0179B, from MO-Sci Corporation) of diameter 40 to80 microns were added to the beaker. A Premier mill dispersator 2000running at 6000 RPM with a black Norblade polyethylene 1.75 inchimpeller were used to further disperse the graphenic carbon particles.Extra n-butyl acetate was added at intervals to maintain properviscosity of mill base in the beaker and maintain a “rolling doughnut”shape of the mill base around the spinning milling blade. The dispersionwas milled in the beaker for 15 hours. The final product was obtained byfiltering off the glass beads through a nylon mesh filter bag (33-NMO 1X1R-RB, from Brown and O'Malley Co.) The final dispersion had totalsolids of 14.18 weight %, resin solids of 10.51 weight %, and grapheniccarbon particles content of 3.67 weight %.

Example 2

A dispersion of thermally produced graphenic carbon particles wasproduced by adding 33.85 g of solvent-born block copolymer dispersant(which comprises 43 weight % n-butyl acetate and 57 weight % blockcopolymer as disclosed in U.S. 2008/0188610), 29.15 g of n-butylacetate, and 7.00 g of thermally produced graphenic carbon particlesproduced in accordance with the method disclosed in U.S. Pat. No.8,486,364 having a measured BET surface area of 280 m²/g into an 8 oz.glass jar along with 350 g of 1.0-1.2 mm Zirconox milling media (fromJyoti Ceramic). The jar was shaken for 4 hours using a Lau disperser(Model DAS 200, Lau, GmbH). The milling media were then separated fromthe dispersion product using paper cone paint filters. The finaldispersion had 37.50 weight % total solids, 27.76 weight % resin solids,and 9.72 weight % graphenic carbon particles.

Example 3

A carbon black pigment dispersion was produced by making apre-dispersion in a Premier PSM-11 basket mill, using 0.8-1.0 Zirconoxmilling media (from Jyoti Ceramic). The ingredients were 7.55 lbs. ofsolvent-born block copolymer dispersant (which comprises 43 weight %n-butyl acetate and 57 weight % block copolymer as disclosed inU.S.2008/0188610), 12.12 lbs. of n-butyl acetate, and 3.02 lbs. ofcarbon black pigment (Emperor 2000 from Cabot Corporation). It wasmilled for 60 minutes to a Hegman of 6.5 to 7. Another 5.0 lbs. ofn-butyl acetate were added as basket mill wash. The pre-dispersion wastransferred to a QM-1 mill (from Premier Mill) and was run at a millspeed of 3000 RPM with a product temperature of 121° F. with 0.3 mm YTZmilling media (from Tosoh Corporation) for 40 minutes of residence time.The final dispersion was 33.24 weight % total solids, 24.70 weight %resin solids, and 8.54 weight % carbon black pigment.

Example 4

A carbon black pigment dispersion was produced by adding 33.85 g ofsolvent-born block copolymer (which comprises 43 weight % n-butylacetate and 57 weight % block copolymer as disclosed in U.S.2008/0188610), 29.15 g of n-butyl acetate, and 7.00 g of carbon blackpigment (Monarch 1300, from Cabot Corporation) into an 8 oz. glass jaralong with 350 g of 1.0-1.2 mm Zirconox milling media (from JyotiCeramic). The jar was shaken for 4 hours using a Lau disperser (ModelDAS 200, Lau, GmbH). The milling media were then separated from thedispersion product using paper cone paint filters. The final dispersionhad 36.30 weight % total solids, 28.72 weight % resin solids, and 7.61weight % carbon black pigment.

Example 5

To evaluate the opacity and absorption of graphenic carbon particles, atinted coating was made comprising 20.00 g of solvent-born blockcopolymer (which comprises 40.83 weight % n-butyl acetate and 59.17weight % block copolymer as disclosed in U.S. 2008/0188610), 1.64 g ofthe dispersion from Example 1, and 5.17 g of n-butyl acetate. This wasthoroughly mixed and then drawn down using a #44 wire wound draw downbar (from R. D. Specialties) onto a black/white opacity chart (ChartPA-2812, from BYK-Gardner). The film was baked in an oven for 30 minutesat 212° F. The final dried film had a thickness of 20 microns andcontained 0.5 weight % of the graphenic carbon particles. The absorptionspectrum of the draw down film is shown in FIG. 5. FIG. 6 includes aphotograph of the film (labeled as Example 5), illustrating the darkappearance of the film.

Example 6

To evaluate the opacity and absorption of graphenic carbon particles, atinted coating was made comprising 20.00 g of solvent-born blockcopolymer (which comprises 40.83 weight % n-butyl acetate and 59.17weight % block copolymer as disclosed in U.S.2008/0188610), 0.60 g ofthe dispersion from Example 2, and 6.21 g of n-butyl acetate. This wasthoroughly mixed and then drawn down using a #44 wire wound draw downbar (from R. D. Specialties) onto a black/white opacity chart (ChartPA-2812, from BYK-Gardner). The film was baked in an oven for 30 minutesat 212° F. The final dried film had a thickness of 20 microns andcontained 0.5 weight % of the graphenic carbon particles. The absorptionspectrum of the draw down film is shown in FIG. 5. FIG. 6 includes aphotograph of the film (labeled as Example 6), illustrating the darkappearance of the film.

Example 7

A comparative example to Examples 5 and 6 was made by making a tintedcoating containing carbon black pigment. The tinted coating was made bymixing together 20.00 g of solvent-born block copolymer (which comprises40.83 weight % n-butyl acetate and 59.17 weight % block copolymer asdisclosed in U.S. 2008/0188610), 0.69 g of the dispersion from Example3, and 6.13 g of n-butyl acetate. This was drawn down using a #44 wirewound draw down bar (from R. D. Specialties) onto a black/white opacitychart (Chart PA-2812, from BYK-Gardner). The film was baked in an ovenfor 30 minutes at 212° F. The final dried film had a thickness of 20microns and contained 0.5 weight % of the carbon black pigment. Theabsorption spectrum of the draw down film is shown in FIG. 5. FIG. 6includes a photograph of the film (labeled as Example 7), illustratingthe relatively light appearance of the film. Visual comparison of thedraw downs (FIG. 6) and comparison of the data (FIG. 5) show that thethermally produced graphenic carbon particles are hiding better and aremore neutrally colored (gray rather than brown) than carbon blackpigment.

Example 8

A comparative example to Example 5 and 6 was made by making a tintedcoating containing a carbon black pigment. The tinted coating was madeby mixing together 20.00 g of solvent-born block copolymer (whichcomprises 40.83 weight % n-butyl acetate and 59.17 weight % blockcopolymer as disclosed in U.S. 2008/0188610), 0.58 g of the dispersionfrom Example 4, and 6.23 g of n-butyl acetate. This was drawn down usinga #44 wire wound draw down bar (from R. D. Specialties) onto ablack/white opacity chart (Chart PA-2812, from BYK-Gardner). The filmwas baked in an oven of 30 minutes at 212° F. The final dried film had athickness of 20 microns and contained 0.5 weight % of the carbon blackpigment. The absorption spectrum of the draw down film is shown in FIG.5. FIG. 6 includes a photograph of the film (labeled as Example 8),illustrating the relatively light appearance of the film. Visualcomparison of the draw downs (FIG. 6) and comparison of the data (FIG.5) show that the thermally produced graphenic carbon particles arehiding better and are more neutrally colored (gray rather than brown)than carbon black pigment.

FIG. 5 is a graph of absorbance versus wavelength for the filmsdescribed in Examples 5 through 8. Specifically, the absorbance spectralabeled Example 5 and Example 6 in FIG. 5 were obtained using the drawdown samples from Examples 5 and 6 with 20 micron-thick coatingscontaining 0.5 weight percent graphenic carbon particles, as describedin those examples. The absorbance spectra labeled Example 7 and Example8 in FIG. 5 were obtained using the draw down samples from Examples 7and 8 with coatings containing carbon black, as described in thoseexamples.

The absorbance values were obtained by measuring the reflectance atwavelengths from 400 to 700 nm at 10 nm intervals using an X-Rite Colori7 spectrophotometer, of the pigmented films over the black and whiteportions of the substrate. In addition, the reflectance values of theblack and white portions of the substrate itself were similarlymeasured. Using all of these reflectance values of the films and of theblack and white portions of the substrate, the reflectance andtransmittance of the pigmented films themselves (in the absence of asubstrate) were derived using the equation R_(m)=R₁+(T₁ ²R₂)/(1−R₁R₂),which is Equation 16 from Wen-Dar Ho, Chen-Chi M. Ma, and Lieh-Chun Wu,“Diffuse Reflectance and Transmittance of IR Absorbing Polymer Film”,Polymer Engineering and Science, October 1998, Volume 38, No. 10. Thisequation, applied to the film measured over the white portion of thesubstrate is R_(mw)=R+(T²R_(w))/(1−RR_(w)), where R_(mw) is the measuredreflectance of the film over the white portion of the substrate, R isthe actual reflectance of the pigmented film in the absence of thesubstrate, T is the actual transmittance of the pigmented film in theabsence of the substrate, and R_(w) is the measured reflectance of thewhite portion of the substrate. This equation, applied to the filmmeasured over the black portion of the substrate isR_(mb)=R+(T²R_(b))/(1−RR_(b)), where R_(mb) is the measured reflectanceof the film over the black portion of the substrate, R is the actualreflectance of the pigmented film in the absence of the substrate, T isthe actual transmittance of the pigmented film in the absence of thesubstrate, and R_(b) is the measured reflectance of the black portion ofthe substrate. With the measured reflectances, we can solve thisequation for the two unknowns: R and T. Namely,R=(R_(w)R_(mb)−R_(b)R_(mw))/[R_(w)−R_(b)−R_(w)R_(b)(R_(mw)−R_(mb))] andT=SQRT{(R_(mw)−R)/[R_(w)(1−RR_(w))]}, where SQRT is the square rootfunction. Then, using Kirchoff's law (R+T+A=1, or written as percentages% R+% T+% A=100), where R is the reflectance, T is the transmittance,and A is the absorbance, or where % R is the percent reflectance, % T isthe percent transmittance, and % A is the percent absorbance, theabsorbance was calculated from the derived R and T values at eachwavelength. In addition to demonstrating higher absorbances for theExample 5 and Example 6 samples throughout the visible range of 400 to700 nm, the results shown in FIG. 5 also demonstrate that the Example 5and Example 6 samples have less variance in their absorbances within thevisible range, e.g., the highest and lowest absorbance values forspecific wavelengths within the 400 to 700 nm range are well below 10percent for the Example 5 and Example 6 samples as demonstrated by theirrelatively flat and horizontal plots. While the results shown in FIG. 5correspond to wavelengths in the visible region (400 to 700 nm), it isto be understood that the use of the present graphenic carbon particlesin coatings and other materials may also result in improved propertiesin other regions, including the UV region and/or IR region.

Example 9

FIG. 7 illustrates a backlit coating sample comprising thermallyproduced graphenic carbon particles as an absorptive pigment, filmforming resins primarily consisting of polyester and melamine, andinorganic pigments primarily consisting of TiO₂ and barytes. The coatingsample was spray applied on to glass at a final dry film thickness of1.1-1.2 mils. The sample was backlit via LED lighting directly on to theuncoated glass side and photographed in a dark room.

FIG. 8 illustrates a backlit coating sample comprising a carbon blackpigment prepared identically to the coating sample shown in FIG. 7, withthe exception that the thermally produced graphenic carbon particleswere replaced with carbon black pigment. Sample preparation, resinformulation, film application and final dry film thickness wereidentical to that of the coating sample illustrated in FIG. 7. Thesample was backlit via LED lighting directly on to the uncoated glassside and photographed in a dark room.

As shown by comparing the backlit coating samples in FIGS. 7 and 8, thecoating comprising the thermally produced graphenic carbon particleblack pigment exhibits superior opacity and absorption in comparisonwith the coating comprising carbon black.

Example 10

Thermally produced graphenic carbon particles produced as in Example 1were dispersed in tetrahydrofuran (THF) at various concentrations of0.005 mg/ml, 0.01 mg/ml and 0.02 mg/ml using bath sonication for 1-3hours (VWR Aquasonic HT250 bath sonicator). Spectrographic absorbancecharacteristics at UV, visible and near IR wavelengths were measured.The results are shown in FIG. 9. High absorbance is demonstrated in theshort wavelength UV region, visible region, and near IR region of thespectrum.

Example 11

For comparison purposes, non-thermally produced graphene made fromexfoliated graphite (GNP) was dispersed in a similar manner as thethermally produced graphenic carbon particles described in Example 10.The comparative GNP graphene particles were prepared by acidintercalation, thermal shock exfoliation and bath sonication. Suchexfoliated GNPs were further exfoliated in a liquid phase by strongprobe sonication and subsequent centrifugation (GNP-EX). Such exfoliatedGNPs were also used as the starting material in a Hummers oxidationprocess to produce graphite oxide (GO), which was converted into reducedgraphite oxide (RGO) using hydrazine, or into octadecylaminefunctionalized graphite (ODA-G). Such types of exfoliated graphemeparticles were dispersed in THF at concentrations of 0.01 mg/ml usingbath sonication for comparison with the 0.01 mg/ml concentration ofthermally produced graphic carbon particles of Example 10. Absorbanceresults are plotted in FIG. 10, which demonstrates significantlyincreased absorbance throughout the 400-1,400 nm wavelength region forthe thermally produced graphenic carbon particle dispersion (labeled asPPGG in FIG. 10) in comparison with the comparative dispersionscontaining exfoliated graphene (labeled as GNP, GNP-EX, RGO and ODA-G inFIG. 10).

The absorption spectra plots shown in FIGS. 9 and 10 were prepared as afunction of concentration using a Varian Cary 5000 spectrophotometerusing cuvettes of 10 mm light path.

For purposes of this detailed description, it is to be understood thatthe invention may assume various alternative variations and stepsequences, except where expressly specified to the contrary. Moreover,other than in any operating examples, or where otherwise indicated, allnumbers expressing, for example, quantities of ingredients used in thespecification and claims are to be understood as being modified in allinstances by the term “about”. Accordingly, unless indicated to thecontrary, the numerical parameters set forth in the followingspecification and attached claims are approximations that may varydepending upon the desired properties to be obtained by the presentinvention. At the very least, and not as an attempt to limit theapplication of the doctrine of equivalents to the scope of the claims,each numerical parameter should at least be construed in light of thenumber of reported significant digits and by applying ordinary roundingtechniques.

Notwithstanding that the numerical ranges and parameters setting forththe broad scope of the invention are approximations, the numericalvalues set forth in the specific examples are reported as precisely aspossible. Any numerical value, however, inherently contains certainerrors necessarily resulting from the standard variation found in theirrespective testing measurements.

Also, it should be understood that any numerical range recited herein isintended to include all sub-ranges subsumed therein. For example, arange of “1 to 10” is intended to include all sub-ranges between (andincluding) the recited minimum value of 1 and the recited maximum valueof 10, that is, having a minimum value equal to or greater than 1 and amaximum value of equal to or less than 10.

In this application, the use of the singular includes the plural andplural encompasses singular, unless specifically stated otherwise. Inaddition, in this application, the use of “or” means “and/or” unlessspecifically stated otherwise, even though “and/or” may be explicitlyused in certain instances.

It will be readily appreciated by those skilled in the art thatmodifications may be made to the invention without departing from theconcepts disclosed in the foregoing description. Accordingly, theparticular embodiments described in detail herein are illustrative onlyand are not limiting to the scope of the invention.

We claim:
 1. An absorptive coating comprising: a resin film; and anabsorptive pigment comprising thermally produced graphenic carbonparticles in an amount up to 20 weight percent based on the total dryfilm weight of the coating, wherein the absorptive coating has a minimumabsorbance of 80 percent throughout a wavelength range of 400 to 1,400nm.
 2. The absorptive coating of claim 1, wherein the thermally producedgraphenic carbon particles comprise from 0.01 to 5 weight percent. 3.The absorptive coating of claim 1, wherein the minimum absorbance isgreater than 85 percent.
 4. The absorptive coating of claim 1, whereinthe thermally produced graphenic carbon particles are produced from ahydrocarbon precursor material capable of forming a two-carbon-fragmentspecies or a hydrocarbon material comprising methane introduced into athermal zone at a temperature of greater than 3,500° C.
 5. Theabsorptive coating of claim 1, wherein the thermally produced grapheniccarbon particles have an average aspect ratio greater than 3:1, a B.E.T.specific surface area of greater than 70 m²/g, and a Raman spectroscopy2D/G peak ratio of at least 0.9:1.
 6. The absorptive coating of claim 1,wherein the resin film comprises a thermoset or thermoplastic filmforming resin.
 7. The absorptive coating of claim 1, wherein theabsorptive coating is applied on a substrate.
 8. The absorptive coatingof claim 7, further comprising at least one intermediate coating betweenthe absorptive coating and the substrate.
 9. The absorptive coating ofclaim 8, wherein the at least one intermediate coating comprises aprimer coating or a color coating.
 10. The absorptive coating of claim7, further comprising a top coating applied on at least a portion of theabsorptive coating.
 11. The absorptive coating of claim 10, wherein thetop coating comprises a color coating or a clear coating.
 12. Anabsorptive coating composition comprising: a solvent; a film-formingresin; and thermally produced graphenic carbon particles in an amount upto 20 weight percent of the total solids weight of the film-formingresin and the thermally produced graphenic carbon particles, wherein theabsorptive coating composition has a minimum absorbance of 80 percentthroughout a wavelength range of 400 to 1,400 nm when cured.
 13. Theabsorptive coating composition of claim 12, wherein the thermallyproduced graphenic carbon particles comprise from 0.01 to 5 weightpercent.
 14. The absorptive coating composition of claim 12, wherein thethermally produced graphenic carbon particles have an average aspectratio greater than 3:1, a B.E.T. specific surface area of greater than70 m²/g, and a Raman spectroscopy 2D/G peak ratio of at least 0.9:1. 15.The absorptive coating composition of claim 12, wherein the film-formingresin comprises a thermoset or thermoplastic film forming resin.
 16. Anarticle comprising: a matrix material; and an absorptive pigmentdispersed in the matrix material comprising thermally produced grapheniccarbon particles in an amount up to 20 weight percent based on the totalweight of the matrix material and the thermally produced grapheniccarbon particles, wherein the article has a minimum absorbance of 80percent throughout a wavelength range of 400 to 1,400 nm.
 17. Thearticle of claim 16, wherein the thermally produced graphenic carbonparticles comprise from 0.01 to 10 weight percent.
 18. The article ofclaim 16, wherein the matrix material comprises a polymer.
 19. A methodof making an absorptive coating composition comprising dispersingthermally produced graphenic carbon particles and a film-forming resinin a solvent, wherein the thermally produced graphenic carbon particlescomprise up to 20 weight percent of the total solids weight of thefilm-forming resin and the thermally produced graphenic carbonparticles, and the absorptive coating composition has a minimumabsorbance of 80 percent throughout a wavelength range of 400 to 1,400nm when cured.
 20. The method of claim 19, wherein the thermallyproduced graphenic carbon particles are produced by introducing amethane precursor material or a hydrocarbon precursor material capableof forming a two-carbon-fragment species into a thermal zone having atemperature of greater than 3,500° C.